INTERNATIONAL TELECOMMUNICATION UNION

TELECOMMUNICATION

STANDARDIZATION SECTOR

STUDY PERIOD 2017-2020

TD82R1 (PLEN/15)

STUDY GROUP 15

Original: English

Question(s): 13/15 Geneva, 19 – 30 June, 2017

TD

Source: Editor, G.8271

Title: Draft Amendment 1 to Recommendation G.8271 – draft for consent

Purpose:

Contact: Tim Frost

Calnex Solutions Ltd.

UK

Tel: +44 7825 706952

Email: tim.frost@calnexsol.com

.

Abstract

This document contains the draft of Amendment 1 to the ITU-T Recommendation G.8271 that was

agreed by Q13 during the meeting in Geneva, 19 – 30 June, 2017.

It is intended for consent at the SG15 plenary meeting, June 2017.

- 2 -

TD82R1 (PLEN/15)

Draft Amendment 1 to Recommendation ITU-T G.8271/Y.1366 (2016)

Time and phase synchronization aspects of telecommunications networks:

Amendment 1

Summary

Amendment 1 to Recommendation ITU-T G.8271 (2016) provides the following updates:

− Updated Title and Scope

− Updated Conventions clause

− Updated Table 1 and addition of Table 2, describing applications for high-accuracy time

synchronization

− Revised notes in clause 7 and 7.1

− Revised clause 8, updating reference point descriptions

− Correction to the definition of the FCS field in the serial communication channel

− Replacement of Table A.7 with a new version and associated notes

− Revision to Tables II.1 and II.2 of Appendix II

− Correction to Appendix V

Note to ITU Editor: Figures 4 and 5 have been changed from the original published version by

editing them as a picture, since the source for the published version is not available. Please ensure

that the new version of the figures are used (i.e. don’t put back the original figures from the current

published version).

- 3 -

TD82R1 (PLEN/15)

Draft Amendment 1 to Recommendation ITU-T G.8271/Y.1366 (2016)

Time and phase synchronization aspects of telecommunications networks:

Amendment 1

1 Title

The title of this Recommendation has been changed to “Time and phase synchronization aspects of

telecommunications networks.”

2 Clause 1: Scope

Replace the text of clause 1 with the following:

This Recommendation defines time and phase synchronization aspects in telecommunications

networks. It specifies the suitable methods to distribute the reference timing signals that can be used

to recover the phase synchronization and/or time synchronization according to the required quality.

It also specifies the relevant time and phase synchronization interfaces and related performance.

The telecommunications networks that are in the scope of this Recommendation are currently

limited to the following scenarios:

• Ethernet ([IEEE 802.3] and [IEEE 802.1Q]).

• MPLS ([IETF RFC 3031] and [ITU-T G.8110]).

• IP ([IETF RFC 791] and [RFC 2460]).

• OTN (ITU-T G.709).

The physical layers that are relevant to this specification are the Ethernet media types, as defined in

[IEEE 802.3] and, for OTN, the Optical OCh layer with OTU frame as defined in [ITU-T G.709].

3 Clause 5: Conventions

Replace the text of clause 5 with the following:

Within this Recommendation, the following conventions are used: The term precision time protocol

(PTP) is the protocol defined by [IEEE 1588]. As an adjective, it indicates that the modified noun is

specified in or interpreted in the context of [IEEE 1588].

4 Clause 6

Replace Table 1 and subsequent text in clause 6 with the following:

- 4 -

TD82R1 (PLEN/15)

Table 1 – Time and phase requirement classes

Level of accuracy Time error requirements

(Note 1)

Typical applications

(for information)

1 500 ms Billing, alarms

2 100 s IP Delay monitoring

Asynchronous Dual Connectivity

3 5 s LTE TDD (large cell)

Synchronous Dual Connectivity (for up to 7 km

propagation difference between eNodeBs)

4 1.5 s UTRA-TDD, LTE-TDD (small cell)

Wimax-TDD (some configurations)

Synchronous Dual Connectivity (for up to 9 km

propagation difference between eNodeBs)

5 1 s Wimax-TDD (some configurations)

6 x ns

(Note 3)

Various applications, including Location based services

and some LTE-A features

(Note 2)

NOTE 1 – The requirement is expressed in terms of error with respect to a common reference.

NOTE 2 – The performance requirements of the LTE-A features are under study. For information purposes

only, values between 500 ns and 1.5 s have been mentioned for some LTE-A features. Depending on the

final specifications developed by 3GPP, LTE-A applications may be handled in a different level of

accuracy.

NOTE 3 – For the value x, refer to Table 2 below and Table II.2 of Appendix II.

Based on Table II.2, it is possible to classify the class 6 level of accuracy into further three sub-

classes, as shown in Table 2 below.

Table 2 – Time and phase requirements for cluster based synchronisation

Level of accuracy

Maximum Relative

Time error

requirements

(Note 1)

Typical applications

(for information)

6A 260ns Intra-band non-contiguous carrier aggregation

with or without MIMO or TX diversity, and

inter-band carrier aggregation with or without

MIMO or TX diversity

6B 130ns Intra-band contiguous carrier aggregation,

with or without MIMO or TX diversity

6C 65ns

MIMO or TX diversity transmissions, at each

carrier frequency

NOTE 1 – The maximum relative time error requirements represent the peak-to-peak time

difference measured between the elements in the cluster only. See Appendix VII of [ITU-T

G.8271.1] for illustration of how requirements are specified in a cluster. In 3GPP terminology

this is equivalent to time alignment error (TAE), which is defined as the largest timing difference

between any two signals.

- 5 -

TD82R1 (PLEN/15)

This Recommendation deals mainly with the Class 4, 5 6A level of accuracy requirements,

indicated as in Table 2.

5 Clause 7

Replace the following text at the end of clause 7:

NOTE – The use of packet-based methods without timing support of intermediate nodes, and the

definition of which class of requirements in Table 1 they can support, are for further study.

The following clauses provide details on the characteristics for the different synchronization

methods.

With the following:

NOTE 1 – additional solutions may be considered as a complement to the above solutions. As an

example, timing may be carried over the radio interface of mobile systems. Applicability to the

general HRMs is for further study.

NOTE 2 – The use of packet-based methods with limited timing support, or without timing support

of intermediate nodes, is considered capable of addressing applications corresponding to class 4.

The following clauses provide details on the synchronization methods based on the distributed

PRTC approach, and packet based methods with timing support of intermediate nodes.

6 Clause 7.1

Replace the last sentence of clause 7.1:

In terms of performance, the accuracy that can be achieved by means of a PRTC system is for

further study.

with the following:

In terms of performance, the accuracy that can be achieved by means of a PRTC system is defined

in [ITU G.8272].

7 Clause 8

Replace clauses 8 and 8.1 with the following:

8 Network reference model

Figure 4 describes the network reference model used to define the time and phase synchronization

performance objectives when the reference timing signal is carried over the transport network:

- 6 -

TD82R1 (PLEN/15)

Figure 4 – Network reference model

The following reference points are defined. All the requirements related to these reference points

are defined with respect to a common time reference, i.e., any recognized time reference such as

GPS time.

• A: PRTC output

• B: Packet master clock output

• C: Packet slave clock input

• D: Packet slave clock output

• E: End application output

Some specific access technologies may need to be considered in the network reference model in

some cases. For instance, the network between points B and C can be composed in some cases of a

transport part and an access part. Each part would then have its own phase/time budget derived

from the media specific mechanisms that have been developed to transport frequency and time

synchronization.

NOTE 1 – In Figure 4 the packet master clock could correspond to a T-GM and the packet slave clock could

correspond to a T-TSC (telecom time slave clock).

NOTE 2 – The performance studies documented in [ITU-T G.8271.1] are based on a full timing support in

the network with hardware timestamping (e.g., T-BC in every node in the case of [IEEE 1588]), and with

physical layer frequency synchronization support (e.g., synchronous Ethernet support). The case of partial

timing support, where some or all of the nodes are not capable of providing timing support to the PTP layer,

is covered in [ITU-T G.8271.2].

NOTE 3 – Some specific access technologies may need to be considered in the network reference model in

some cases. For instance, the packet network between points R2 and R3 can be composed in some cases of a

transport part and an access part. Each part would then have its own phase/time budget. In some radio access

networks (RAN) scenarios, for instance when the RAN is split based on different radio functions, from the

point of view of timing, the starting point for the RAN may be present between points B and C shown in

Figure 4. Alternatively, the entire network model may be present within the RAN. Details are for further

study.

NOTE 4 – Additional detail for the network reference model of Figure 4 for the case of PTP over non-packet

technologies (e.g. OTN, GPON, microwave) is for further study.

The overall budget relates to measurement point 'E' (i.e., the time error at E with respect to the

common time reference).

- 7 -

TD82R1 (PLEN/15)

'A', 'B', 'C' and 'D' define the other relevant measurement reference points and related network

limits, that also indicate the budget of the noise that can be allocated to the relevant network

segments (e.g., 'A to C', 'A to D', etc.).

The measurement points that are of interest for a specific application may depend on where the

network administrative domain borders apply.

Also, as described above, the measurement in some cases needs to be performed on a two-way

timing signal, which would require a specific test set-up and metrics to be used.

The measurement set-up for two-way timing signals as well as the noise that can be added by the

measurement test equipment is an item for further study.

Another possibility is to perform the measurement using an external dedicated output phase/time

reference, such as a 1PPS interface. Annex A in this Recommendation provides guidance about this

type of interface.

8.1 Access section of HRM with PTP/native access IWF

The general network reference model in Figure 4 can be further expanded to illustrate different

types of access technology that may be used at the edge of the network such as microwave, DSL or

PON.

Generally access technologies can be categorized as either point-to-multipoint shared technologies

or point-to-point technologies. An example of a point-to-multipoint shared media technology is a

PON with a single multi-port head end and multiple end devices. An example of a point to point

technology is a microwave system. Figure 5 expands the access section to show the media

conversion that occurs between the Ethernet technology that forms the existing synchronization

HRM of the transport section and the technologies in the access section of the HRM. The time error

budget of this section may depend on the specific type of technology.

Figure 5 – Network reference model with access section

- 8 -

TD82R1 (PLEN/15)

For example, between B.0 and B.1 the transport section consists of a network chain from

[ITU-T G.8271.1] comprised of full timing aware ITU-T G.8273.2 T-BCs using PTP & SyncE.

Between B.1 and C of the access section, there may also be T-BCs, and in this case they are

connected to and from native access clocks. These native access clocks provide the direct

connection to the medium. Essentially, the T-BC and native access clock provides an Interworking

Function (IWF) that converts between Ethernet carrying PTP and the access medium.

The access section will have a time error that is a combination of the constant and dynamic

components of the medium as well as contribution from the clocks in the access section.

8 Annex A

Replace point 5 in clause A.1.3.2 with the following:

5. FCS

The FCS has one octet. The checksum includes message Header, Length and Payload

fields. The polynomial for generating FCS is G(x) = x8 + x5 + x4 + 1. The initial value of the

field should be set to 0xFF. The right shift operation should be used. There should be no bit

inversion of the input and output value. The transmission of the octet should follow the

same bit order as other data octets.

Further details are for further study.

9 Annex A

Replace Table A.7 with the following table and associated notes:

Table A.7 – GNSS status message payload

Offs

et

Length

(octets) Name Notes

0 1 Types of time source

0x00: Beidou (Compass)

0x01: GPS

0x02: PTP

0x03: Galileo

0x04: Glonass

0x05: QZSS

0x06: IRNSS

0x07: GNSS (Combination of constellations)

0x08: Unknown (in case there is no information

about which GNSS timescale is really used and

no possible action to compel the module to

work with a specific GNSS timescale)

0x09 ~ 0xFF: Reserved

1 1 Status of time source

GNSS Fix Type:

0x00: Position unknown

0x01: dead reckoning only (see Note 1)

0x02: 2D-fix

0x03: 3D-fix

- 9 -

TD82R1 (PLEN/15)

Table A.7 – GNSS status message payload

Offs

et

Length

(octets) Name Notes

0x04: GNSS + dead reckoning combined

0x05: Time only fix

0x06: A-GNSS

0x07: GNSS + SBAS

0x08: GNSS + GBAS

0x09 ~ 0xFF: reserved

3 2 Alarm Status Monitor

Time source alarm status:

Bit 0: not used

Bit 1: Antenna open

Bit 2: Antenna shorted

Bit 3: Not tracking satellites

Bit 4: Reserved

Bit 5: Survey-in progress

Bit 6: no stored position

Bit 7: Leap second pending

Bit 8: In test mode

Bit 9: GNSS solution (i.e., derived position and

time) is uncertain (see Note 2)

Bit 10: Reserved

Bit 11: Almanac not complete

Bit 12: PPS was generated

Bit 13 ~ Bit 15: Reserved

4 4 Reserved Reserved

NOTE 1: Dead Reckoning Only – Position from GNSS is lost. Current position is estimated from the last-

known position, plus knowledge of the velocity and acceleration of the antenna since the GNSS-based

position was known.

NOTE 2: GNSS solution is uncertain. When this bit is 1, it indicates that the accuracy of the position derived

from GNSS is uncertain, possibly due to not being able to see enough satellites. This alarm may indicate that

the antenna has been moved or fallen from place since the unit completed the last self-survey.

10 Appendix II

Table II.1 should be replaced with the new version below:

- 10 -

TD82R1 (PLEN/15)

Table II.1 – Time and phase end-application requirements

Application/

Technology

Accuracy Specification

CDMA2000 ±3 µs with respect to CDMA System Time, which uses

the GPS timescale (which is traceable and synchronous

to UTC except for leap second corrections)

±10 µs with respect to CDMA System Time for a

period not less than 8 hours (when the external source

of CDMA system time is disconnected)

[b-3GPP2 C.S0002]

section 1.3

[b-3GPP2 C.S0010]

section 4.2.1.1

TD-SCDMA

(NodeB TDD

mode)

3 µs maximum deviation in frame start times between

any pair of cells on the same frequency that have

overlapping coverage areas

[b-3GPP TS 25.123]

section 7.2

WCDMA-TDD

(NodeB TDD

mode)

In TDD mode, to support Intercell Synchronization

and Handoff, a common timing reference among

NodeB is required, and the relative phase difference of

the synchronization signals at the input port of any

NodeB in the synchronized area shall not exceed

2.5 s

[b-3GPP TS 25.402]

sections 6.1.2 and 6.1.2.1

W-CDMA

MBSFN

12.8 µs for MBMS over a single frequency network,

where the transmission of NodeB is closely time

synchronized to a common reference time

[b-3GPP TS 25.346]

sections 7.1A and 7.1B.2.1

LTE MBSFN Values < ±1 µs with respect to a common time

reference (continuous timescale) have been mentioned

Under study

W-CDMA

(Home NodeB

TDD mode)

Microsecond level accuracy (no hard requirement

listed)

[b-3GPP TR 25.866]

section 8

WiMAX 1) The downlink frames transmitted by the serving

base station and the Neighbour base station shall be

synchronized to a level of at least 1/8 cyclic prefix

length (which is equal to 1.428 µs).

At the base station, the transmitted radio frame shall

be time-aligned with the 1PPS timing pulse

2) The base station transmit reference timing shall be

time-aligned with the 1PPS pulse with an accuracy

of ± 1 µs

[b-IEEE 802.16]

Table 6-160,

section 8.4.13.4

[b-WMF T23-001]

section 4.2.2

LTE-TDD

(Wide-Area Base

station)

3 µs for small cell (< 3 km radius)

10 µs for large cell (> 3 km radius)

maximum absolute deviation in frame start timing

between any pair of cells on the same frequency that

have overlapping coverage areas

[b-3GPP TS 36.133]

section 7.4.2

- 11 -

TD82R1 (PLEN/15)

Table II.1 – Time and phase end-application requirements

Application/

Technology

Accuracy Specification

LTE-TDD

(home-area base

station)

1) 3 µs for small cell (< 500m radius). For large cell

(> 500 m radius), 1.33 + Tpropagation s time

difference between base stations,

where Tpropagation is the propagation delay between

the Home base station and the cell selected as the

network listening synchronization source. In terms

of the network listening synchronization source

selection, the best accurate synchronization source

to GNSS should be selected. If the Home base

station obtains synchronization without using

network listening, the small cell requirement

applies.

2) The requirement is 3.475 µs but in many scenarios

a 3 µs sync requirement can be adopted.

[b-3GPP TS 36.133]

section 7.4.2

[b-3GPP TR 36.922]

section 6.4.1.2

LTE-TDD to

CDMA 1xRTT

and HRPD

handovers

eNodeB shall be synchronized to GPS time. With

external source of CDMA system time disconnected,

the eNodeB shall maintain the timing accuracy within

±10 µs with respect to CDMA system time for a period

of not less than 8 hours

[b-3GPP TS 36.133]

section 7.5.2.1

LTE-A Phase/Time requirements for the applications listed

below are currently under study:

• Carrier aggregation

• Coordinated multipoint transmission (also known as

Network-MIMO)

• Relaying function

[b-3GPP TS 36.814]

IP network delay

monitoring

The requirement depends on the level of quality that

shall be monitored. As an example ±100 µs with

respect to a common time reference (e.g., UTC) may

be required. ±1 ms has also been mentioned

NOTE – There is no

standard requirement yet.

Requirements are operator

dependent (depending on

the application)

Billing and alarms ±100 ms with respect to a common time reference

(e.g., UTC)

NOTE 1 – In the case of mobile applications, the requirements are generally expressed in terms of phase

error between base stations. In the case of a centralized master, the requirement could be expressed as ±

half of the accuracy requirement applicable to the specific technology.

NOTE 2 – The requirements are generally valid during normal conditions. The applicable requirements

during failure conditions are for further study.

Table II.2 should be replaced with the new version below:

- 12 -

TD82R1 (PLEN/15)

Table II.2 – Other time and phase requirements

Typical applications

(for information)

Synchronization

requirements

Specification

Asynchronous dual connectivity (note, applicable only

for FDD-FDD inter-band dual connectivity)

500 µs

(Note 4)

[b-3GPP TS 36.133]

Synchronous dual connectivity (note, applicable only

for TDD-TDD and FDD-FDD inter-band dual

connectivity)

33 µs

(Note 4)

[b-3GPP TS 36.133]

section 7.13 and 7.15.2

Intra-band non-contiguous carrier aggregation with or

without MIMO or TX diversity, and inter-band carrier

aggregation with or without MIMO or TX diversity

260 ns

(Note 3)

[b-3GPP TS 36.104]

section 6.5.3.1

Intra-band contiguous carrier aggregation, with or

without MIMO or TX diversity

130 ns

(Note 3)

[b-3GPP TS 36.104]

section 6.5.3.1

Location Based Services using OTDOA (Note 2) 100 ns

MIMO or TX diversity transmissions, at each carrier

frequency

65 ns

(Note 3)

[b-3GPP TS 36.104]

section 6.5.3.1

More emerging LTE-A features that require multiple

antenna co-operation within a cluster.

x ns

(Note 1) (Note 3)

NOTE 1 – The performance requirements of the LTE-A features are under study. The value for x is for

further study.

NOTE 2 – 100 ns supports approximately 30-40m of location accuracy when using OTDOA with a

minimum of three base stations.

NOTE 3 – The requirements are expressed in terms of time alignment error (TAE) in the 3GPP

specifications, which is defined as the largest timing difference between any two signals (i.e. radio signal

transmitted from base station sectors). In ITU-T terminology, this is equivalent to maximum relative time

error between any two radio signals (i.e. base station sectors), both of which have the same timing

reference. Although phase/time accuracy requirements for CA and CoMP are generic and are not defined

for any particular network topology, this level of phase error budget in general could be achieved by

antennas that are co-located with or connected to the same BBU via direct links. The support of some of

these synchronization requirements for scenarios where the antennas are neither co-located (e.g. as related

to Inter-site carrier aggregation) nor connected via direct links to the same BBU is under study.

NOTE 4- maximum absolute timing mismatch between subframes which are transmitted by Master eNB

(MeNB) and Secondary eNB (SeNB) and are scheduled for the same UE. This means that part of this

budget should be allocated to propagation time difference between MeNB and SeNB. As an example 9 km

propagation difference accounts for approximately 30 µs, which leaves 3 µs time error between the eNBs.

7 km propagation difference accounts for approximately 23 µs, which leaves 10 µs time error between the

eNBs.

11 Appendix V

At the end of Appendix V, replace last equation and the definitions with the followings:

The general term for the delay asymmetry caused by the speed mismatch:

)2

(8()2

(8)( SlaveMasteramblePre

SlaveMasterFCSPKT

VV)L

VVLLsymmetrydelayPathA

(V-8)

Where:

- 13 -

TD82R1 (PLEN/15)

PKTL is the length of the packet (excluding the preamble and FCS) in bytes

FCSL is the length of the packet FCS in bytes

amblePreL

is the length of the packet preamble in bytes

MasterV is the timestamp interface bit period on the PTP Master Clock in seconds/bit

SlaveV is the timestamp interface bit period on the PTP Slave Clock in seconds/bit

______________